When you get it work, install mesa-utils with sudo apt-get install mesa-utils which allows us to recognize the GPU.
Switch to Intel GPU from Prime Indicator and get Intel Graphics Installer, find the Installer in Dash and run it to update your Intel 4000 with latest drivers.

EDIT: After installing the Intel package, if sudo apt-get update will fail on "download.01.org" public key, run this in terminal: